Class 12 Physics Ch-6 Electromagnetic Induction MCQs Exam 2027

Unit 1: Electrostatics

1. The surface density of charge is equal to: [BSEB, 2021 (A)]

   (A) Total Charge / Total Area

   (B) Total Charge $\times$ Total Area

   (C) Total Charge / Total Volume

   (D) Total Charge $\times$ Total Volume

2. The unit of electric intensity is: [BSEB, 2017 (A)]

   (A) Newton/meter

   (B) Volt/meter

   (C) Dyne/cm²

   (D) Volt · meter

3. The sum of charges on the collecting plate and condensing plate of a charged capacitor is: [BSEB, 2020 (A)]

   (A) Zero

   (B) 1 μC

   (C) 1 C

   (D) Infinite

4. The unit of permittivity of free space ($\epsilon_0$) is: [BSEB, 2024 (A)]

   (A) F · m

   (B) F · m⁻¹ (Farad/meter)

   (C) C · V⁻¹

   (D) C² · N · m²

5. The capacitance of a conductor is: [BSEB, 2021 (A)]

   (A) $C = QV$

   (B) $C = Q/V$

   (C) $C = V/Q$

   (D) $C = Q^2V$

6. The electric potential in the equatorial position of an electric dipole is: [BSEB, 2021 (A)]

   (A) $\frac{1}{4\pi\epsilon_o} \frac{p \cos \theta}{r^2}$

   (B) $\frac{1}{4\pi\epsilon_o} \frac{p}{r^2}$

   (C) $\frac{1}{4\pi\epsilon_o} \frac{p}{r}$

   (D) Zero

Unit 2: Current Electricity

7. The power of an electric circuit is: [BSEB, 2020 (A)]

   (A) $V \cdot R$

   (B) $V^2 \cdot R$

   (C) $V^2 / R$

   (D) $V^2 \cdot R \cdot t$

8. In a parallel combination of resistors, which of the following remains constant? [BSEB, 2021 (A)]

   (A) Potential difference

   (B) Current

   (C) Both A and B

   (D) None of these

9. With the increase of temperature, the specific resistance of a semiconductor: [BSEB, 2019 (A)]

   (A) Increases

   (B) Decreases

   (C) Remains unchanged

   (D) Becomes zero

Unit 3: Magnetic Effects of Current & Magnetism

10. Which expression is correct for the Lorentz force? [BSEB, 2022 (A)]

    (A) $\vec{F} = q[\vec{E} + (\vec{v} \times \vec{B})]$

    (B) $\vec{F} = q[\vec{E} – (\vec{v} \times \vec{B})]$

    (C) $\vec{F} = q[\vec{v} + (\vec{E} \times \vec{B})]$

    (D) $\vec{F} = q[\vec{B} + (\vec{v} \times \vec{E})]$

11. The value of the angle of dip at the Earth’s magnetic pole is: [BSEB, 2019 (A)]

    (A) 0°

    (B) 45°

    (C) 90°

    (D) 180°

12. The relation between geometric length ($L_g$) and magnetic length ($L_m$) of a magnet is: [BSEB, 2020 (A)]

    (A) $L_m = \frac{5}{6} L_g$

    (B) $L_m = \frac{6}{5} L_g$

    (C) $L_m = L_g$

    (D) $L_m = 2 L_g$

13. A magnetic field of 5 Tesla is equal to: [BSEB, 2021 (A)]

    (A) $5 \times \text{Weber}/(\text{meter})^2$

    (B) $5 \times 10^5 \, \text{Weber}/(\text{meter})^2$

    (C) $5 \times 10^2 \, \text{Weber}/(\text{meter})^2$

    (D) $5 \times 10^2 \, \text{Weber} \cdot (\text{meter})^2$

14. The dimension of magnetic flux ($\phi$) is: [BSEB, 2023 (A)]

    (A) $[ML^2T^{-2}A^{-1}]$

    (B) $[ML^2T^{-1}A^{-2}]$

    (C) $[MLT^{-2}A^{-1}]$

    (D) $[ML^2T^{-2}A^{-2}]$

15. The working of a dynamo is based on the principle of: [BSEB, 2024 (A)]

    (A) Heating effect of current

    (B) Electromagnetic Induction

    (C) Chemical effect of current

    (D) None of these

16. When a metal sphere is made to oscillate in a magnetic field, its motion is: [BSEB, 2024 (A)]

    (A) Accelerated

    (B) Damped

    (C) Uniform

    (D) None of these

Unit 4: Electromagnetic Induction (EMI) & Alternating Current (AC)

17. In a step-down transformer, which quantity decreases? [BSEB, 2020 (A)]

    (A) Current

    (B) Voltage

    (C) Power

    (D) Frequency

18. The core of a transformer is laminated to: [BSEB, 2024 (A)]

    (A) Obtain high voltage

    (B) Reduce current

    (C) Reduce energy loss due to eddy currents

    (D) Increase magnetic field

19. The S.I. unit of self-inductance is: [BSEB, 2024 (A)]

    (A) Coulomb

    (B) Volt

    (C) Ohm

    (D) Henry

20. The impedance of an $L-R$ circuit is: [BSEB, 2023 (A)]

    (A) $R + \omega L$

    (B) $\sqrt{R^2 + \omega L}$

    (C) $\sqrt{R + \omega^2 L^2}$

    (D) $\sqrt{R^2 + \omega^2 L^2}$

21. Lenz’s law is a consequence of the principle of conservation of: [BSEB, 2022 (A)]

    (A) Charge

    (B) Momentum

    (C) Energy

    (D) Mass

22. In a step-up transformer, if $N_1$ and $N_2$ are number of turns in primary and secondary coils respectively, then: [BSEB, 2021 (A)]

    (A) $N_1 > N_2$

    (B) $N_2 > N_1$

    (C) $N_1 = N_2$

    (D) $N_1 = 0$

23. The S.I. unit of magnetic flux is: [BSEB, 2022 (A)]

    (A) Weber

    (B) Watt

    (C) Tesla

    (D) Joule

24. Inductive Reactance ($X_L$) is equal to: [BSEB, 2024 (A)]

    (A) $\omega L$

    (B) $1/\omega L$

    (C) $\omega/L$

    (D) $L/\omega$

25. Hot wire ammeter measures the: [BSEB, 2020 (A)]

    (A) Peak value of AC

    (B) Average value of AC

    (C) Root Mean Square (rms) value of AC

    (D) None of these

26. The resistance of a closed circuit is 10 Ω. Magnetic flux is $\phi = 6t^2 – 5t + 1$. The current at $t = 0.25$ sec is: [BSEB, 2018 (A)]

    (A) 0.4 A

    (B) 0.2 A

    (C) 2.0 A

    (D) 1.0 A

27. An induction coil is an instrument by which we produce: [BSEB, 2024 (A)]

    (A) High current

    (B) High voltage

    (C) Low current

    (D) Low voltage

28. The power factor of an $L-R$ circuit is: [BSEB, 2023 (A)]

    (A) $R + \omega L$

    (B) $\frac{R}{\sqrt{R^2 + \omega^2 L^2}}$

    (C) $R \sqrt{R^2 + \omega^2 L^2}$

    (D) $\omega L / R$

29. One Henry is equal to: [BSEB, 2021 (A)]

    (A) $10^3 \, mH$

    (B) $10^6 \, mH$

    (C) $10^{-3} \, mH$

    (D) $10^{-6} \, mH$

30. The relation between $I_{rms}$ and peak current $I_0$ is: [BSEB, 2024 (A)]

    (A) $I_{rms} = 0.505 \, I_0$

    (B) $I_{rms} = 0.707 \, I_0$

    (C) $I_{rms} = 0.606 \, I_0$

    (D) $I_{rms} = I_0$

31. If the equation of an AC is $I = 60 \sin(100\pi t)$, the frequency of the current will be: [BSEB, 2021 (A)]

    (A) 50 Hz

    (B) 100 Hz

    (C) 100π Hz

    (D) 60 Hz

32. The dimension of self-inductance is: [BSEB, 2017 (A)]

    (A) $[ML^2T^{-2}A^{-2}]$

    (B) $[ML^2T^{-2}A^{-1}]$

    (C) $[MLT^{-2}A^{-2}]$

    (D) $[ML^2T^{-1}A^{-2}]$

33. A choke coil has self-inductance of 5 H. Current increases at $2 A/s$. Induced emf is: [BSEB, 2023 (A)]

    (A) 2.5 V

    (B) 5 V

    (C) -10 V

    (D) 10 V

34. A transformer is a device used: [BSEB, 2020 (A)]

    (A) To convert DC into AC

    (B) To convert AC into DC

    (C) To increase/decrease DC voltage

    (D) To increase/decrease AC voltage

35. The S.I. unit of mutual inductance is: [BSEB, 2022 (A)]

    (A) Henry

    (B) Ohm

    (C) Tesla

    (D) Weber

36. The power factor of an AC circuit is given by: [BSEB, 2018 (A)]

    (A) $\cos \phi$

    (B) $\sin \phi$

    (C) $\tan \phi$

    (D) $1 \cdot \cos \phi$

37. The unit of Reactance is: [BSEB, 2023 (A)]

    (A) Ohm

    (B) Mho

    (C) Farad

    (D) Ampere

38. The average value of AC over a full cycle is: [BSEB, 2021 (A)]

    (A) Zero

    (B) I/2

    (C) I

    (D) 2I/π

39. Capacitive Reactance ($X_C$) is: [BSEB, 2021 (A)]

    (A) $\omega C$

    (B) $1/\omega C$

    (C) $\omega/C$

    (D) $C/\omega$

40. The natural frequency of an $L-C$ circuit is: [BSEB, 2022 (A)]

    (A) $f = \frac{1}{2\pi \sqrt{LC}}$

    (B) $f = \frac{1}{2\pi} \sqrt{\frac{L}{C}}$

    (C) $f = 2\pi \sqrt{LC}$

    (D) $f = \frac{1}{2\pi} \sqrt{LC}$

41. The power factor of a choke coil is: [BSEB, 2022 (A)]

    (A) 0

    (B) 1

    (C) 0.5

    (D) 2

42. In an AC circuit, the ‘wattless component’ of current is: [BSEB, 2019 (A)]

    (A) $I \cos \phi$

    (B) $I \sin \phi$

    (C) $I \tan \phi$

    (D) $I \cos^2 \phi$

43. Which is correct for the peak value $I_0$ and $I_{rms}$ of AC? [BSEB, 2024 (A)]

    (A) $I_{rms} = \sqrt{2} I_0$

    (B) $I_{rms} = \frac{I_0}{\sqrt{2}}$

    (C) $I_{rms} = 2 I_0$

    (D) $I_{rms} = I_0/2$

44. Choke coil works on the principle of: [BSEB, 2026]

    (A) Self-induction

    (B) Transient current

    (C) Mutual induction

    (D) Wattless current

45. If $L$ and $R$ represent inductance and resistance, then the unit of $L/R$ is: [BSEB, 2026]

    (A) Ohm

    (B) Second

    (C) Volt

    (D) Ampere

46. If the magnetic field is same but area of the loop is increased, the flux: [BSEB, 2026]

    (A) Increases

    (B) Decreases

    (C) Becomes zero

    (D) Remains unchanged

47. An example of natural electromagnetic induction is: [BSEB, 2026]

    (A) Radio

    (B) Television

    (C) Battery charging

    (D) Lightning strike

48. The phenomenon of electromagnetic induction was discovered by:

    (A) Faraday

    (B) Fleming

    (C) Lenz

    (D) Rumkorff

49. If magnetic field $\vec{B}$ is perpendicular to area vector $d\vec{s}$, the magnetic flux on $ds$ will be: [BSEB, 2024 (A)]

    (A) $B \, ds \cos \theta$

    (B) $B \, ds \sin \theta$

    (C) $B \, ds \tan \theta$

    (D) Zero

50. The kinetic energy due to current $i$ flowing in inductance $L$ is:

    (A) Zero

    (B) $\frac{1}{2} L i^2$

    (C) $\frac{1}{2} i L^2$

    (D) $\frac{1}{2} L^2 i^2$

51. The quantity having the same dimension as $\frac{1}{2} \epsilon_0 E^2$ is: [BSEB, 2018 (A)]

    (A) $\frac{B^2}{2\mu_0}$

    (B) $\frac{1}{2} B^2 \mu_0$

    (C) $\mu_0^2/2B$

    (D) $\frac{1}{2} B\mu_0^2/B$

52. The self-inductance of a solenoid is:

    (A) $\mu_0 N^2 A/l$

    (B) $\mu_0 N A^2/l$

    (C) $\mu_0 N^2 A^2/l$

    (D) None

53. A conductor of length $l$ moves with velocity $v$ parallel to magnetic field $B$. Induced emf is:

    (A) $lvB$

    (B) $1/2 \, lvB$

    (C) Zero

    (D) $1/2 \, l^2 vB$

54. A metal sphere becomes hot when moved in a magnetic field because of:

    (A) AC is produced

    (B) DC is produced

    (C) Eddy currents are produced

    (D) Extra current is produced

55. The dimension of $L/R$ is:

    (A) $M^0 L^0 T^1$

    (B) $M^0 L T$

    (C) $M L T^{-2}$

    (D) None

Unit 5: Electromagnetic Waves

56. The nature of electromagnetic waves is: [BSEB, 2020 (A)]

    (A) Transverse

    (B) Longitudinal

    (C) Both A and B

    (D) Electrical

57. The direction of propagation of electromagnetic waves is: [BSEB, 2021 (A)]

    (A) Parallel to $\vec{E}$

    (B) Parallel to $\vec{B}$

    (C) Parallel to $(\vec{B} \times \vec{E})$

    (D) Parallel to $(\vec{E} \times \vec{B})$

58. The energy density of magnetic field $\vec{B}$ is:

    (A) $B^2/2\mu_0$

    (B) $B^2/\mu_0$

    (C) $B^2/4\mu_0$

    (D) $B^2/3\mu_0$

Unit 6: Optics

59. The spectrum of sunlight is: [BSEB, 2026]

    (A) Continuous

    (B) Line spectrum

    (C) Dark line spectrum

    (D) Dark band spectrum

60. The field of view is maximum for: [BSEB, 2026]

    (A) Plane mirror

    (B) Convex mirror

    (C) Concave mirror

    (D) Cylindrical mirror

61. The ratio of refractive index of red light to blue light in air is: [BSEB, 2026]

    (A) Less than one

    (B) Greater than one

    (C) Equal to one

    (D) None of these

62. Refractive index of water is 1.33. Speed of light in water will be: [BSEB, 2026]

    (A) $1.33 \times 10^8 \, m/s$

    (B) $4 \times 10^8 \, m/s$

    (C) $2.25 \times 10^8 \, m/s$

    (D) $3 \times 10^8 \, m/s$

63. The wavefront due to a point source at a finite distance is: [BSEB, 2026]

    (A) Plane

    (B) Circular

    (C) Cylindrical

    (D) Spherical

64. For destructive interference, path difference is equal to: [BSEB, 2026]

    (A) $n\lambda$

    (B) $(2n+1)\lambda/2$

    (C) Zero

    (D) Infinity

65. Lens used to remove hypermetropia is: [BSEB, 2026]

    (A) Convex

    (B) Concave

    (C) Cylindrical

    (D) Plano-convex

66. The inverse square law for intensity of light is valid for: [BSEB, 2026]

    (A) Point source

    (B) Line source

    (C) Cylindrical source

    (D) Plane source

67. Coherent sources are those for which: [BSEB, 2026]

    (A) Phase difference remains constant

    (B) Amplitude remains constant

    (C) Frequency changes

    (D) None of these

68. Natural light from the sun is: [BSEB, 2026]

    (A) Polarized

    (B) Unpolarized

    (C) Partially polarized

    (D) Linearly polarized

69. On increasing the length of the tube of a microscope, its magnifying power: [BSEB, 2026]

    (A) Increases

    (B) Decreases

    (C) Becomes zero

    (D) Remains unchanged

70. The angle of reflection for a ray incident normally on a plane mirror is: [BSEB, 2026]

    (A) 0°

    (B) 90°

    (C) 180°

    (D) 45°

71. Relation between phase difference ($\phi$) and path difference ($\Delta x$) is: [BSEB, 2026]

    (A) $\phi = (2\pi/\lambda) \Delta x$

    (B) $\phi = (\pi/\lambda) \Delta x$

    (C) $\phi = (\lambda/2\pi) \Delta x$

    (D) None of these

72. Cylindrical lens is used for: [BSEB, 2026]

    (A) Myopia

    (B) Hypermetropia

    (C) Astigmatism

    (D) Presbyopia

73. The focal length of the eye lens of a healthy person is about: [BSEB, 2026]

    (A) 1 mm

    (B) 2 cm

    (C) 25 cm

    (D) 1 m

74. For removal of myopia, we use: [BSEB, 2022 (A)]

    (A) Convex lens

    (B) Concave lens

    (C) Cylindrical lens

    (D) Bifocal lens

75. The minimum angle of deviation for a thin prism of refractive index $\mu$ is: [BSEB, 2021 (A)]

    (A) $(1-\mu)A$

    (B) $(\mu-1)A$

    (C) $(\mu+1)A$

    (D) $(1+\mu)A^2$

76. The cause of color of light is: [BSEB, 2024 (A)]

    (A) Its frequency

    (B) Its velocity

    (C) Its amplitude

    (D) Its phase

77. Two lenses of power -15D and +5D are in contact. The focal length of the combination is: [BSEB, 2018 (A)]

    (A) -10 cm

    (B) -10 cm

    (C) +10 cm

    (D) None of these

78. In an astronomical telescope, the final image is: [BSEB, 2024 (A)]

    (A) Real and erect

    (B) Real and inverted

    (C) Virtual and inverted

    (D) Virtual and erect

79. Optical path is equal to: [BSEB, 2024 (A)]

    (A) Refractive index $\times$ path length

    (B) Refractive index / path length

    (C) Path length / refractive index

    (D) Refractive index $\times$ path length / 2

80. The image formed by a simple microscope is: [BSEB, 2021 (A)]

    (A) Virtual and erect

    (B) Virtual and inverted

    (C) Real and erect

    (D) Real and inverted

81. Which phenomenon confirms the transverse nature of light? [BSEB, 2023 (A)]

    (A) Interference

    (B) Diffraction

    (C) Polarization

    (D) Refraction

82. The refractive index of diamond is approximately: [BSEB, 2021 (A)]

    (A) 1

    (B) 1.5

    (C) 2.42

    (D) 4.14

83. Least distance of distinct vision for a normal eye is: [BSEB, 2021 (A)]

    (A) 100 cm

    (B) 50 cm

    (C) 25 cm

    (D) 6.25 cm

84. Brewster’s law is: [BSEB, 2024 (A)]

    (A) $\mu = \sin i_p$

    (B) $\mu = \cos i_p$

    (C) $\mu = \tan i_p$

    (D) $\mu = \tan^2 i_p$

85. A lens ($n=1.5$) has $f=20 \, cm$ in air. In a medium of refractive index 1.5, its focal length will be: [BSEB, 2023 (A)]

    (A) 20 cm

    (B) 40 cm

    (C) 5 cm

    (D) Infinity

86. Wave number is equal to: [BSEB, 2022 (A)]

    (A) $1/\lambda$

    (B) $\lambda$

    (C) $2\pi/\lambda$

    (D) $1/\lambda^2$

87. Power of combination of two lenses of $f=20 \, cm$ and $f=-40 \, cm$ is: [BSEB, 2024 (A)]

    (A) 5 D

    (B) 2.5 D

    (C) -2.5 D

    (D) -5 D

88. The blue color of the sky is due to: [BSEB, 2023 (A)]

    (A) Reflection

    (B) Refraction

    (C) Scattering

    (D) Diffraction

89. The width of interference fringe is: [BSEB, 2021 (A)]

    (A) $\beta = D\lambda/d$

    (B) $\beta = d\lambda/D$

    (C) $\beta = Dd/\lambda$

    (D) $\beta = \lambda/Dd$

90. When a convex lens is immersed in water, it behaves as: [BSEB, 2016 (A)]

    (A) Convex lens

    (B) Concave lens

    (C) Glass plate

    (D) Prism

91. What kind of lines are found in the solar spectrum? [BSEB, 2024 (A)]

    (A) Dark lines (Fraunhofer lines)

    (B) Bright lines

    (C) Dark bands

    (D) None of these

92. The S.I. unit of power of lens is: [BSEB, 2024 (A)]

    (A) Joule

    (B) Dioptre

    (C) Candela

    (D) Watt

93. In Young’s double slit experiment, if $\lambda$ is doubled, the fringe width will be: [BSEB, 2024 (A)]

    (A) Halved

    (B) Doubled

    (C) Unchanged

    (D) Quadrupled

Units 7-9: Modern Physics

94. The order of radius of a nucleus is: [BSEB, 2017 (A)]

    (A) $10^{-10} \, m$

    (B) $10^{-15} \, m$

    (C) $10^{-6} \, m$

    (D) $10^{-8} \, m$

95. Cathode rays are: [BSEB, 2021 (A)]

    (A) Electrons

    (B) Neutrons

    (C) Protons

    (D) Photons

96. Which of the following is correct for a radioactive element? [BSEB, 2021 (A)]

    (A) $T_a = \lambda / 0.6931$

    (B) $T_a = 1/\lambda$ (Mean life)

    (C) $T_a = (0.6931)\lambda$

    (D) $T_a = 1/\lambda^2$

97. Which of the following relations is correct? [BSEB, 2021 (A)]

    (A) $1 \, eV = 1.6 \times 10^{-19} \, J$

    (B) $1 \, eV = 1.6 \times 10^{-18} \, J$

    (C) $1 \, eV = 1.6 \times 10^{19} \, J$

    (D) $1 \, eV = 1.6 \times 10^{-31} \, J$

98. Which of the following particles is chargeless? [BSEB, 2020 (A)]

    (A) Alpha particle

    (B) Beta particle

    (C) Photon

    (D) Proton

99. The majority charge carriers in p-type semiconductors are: [BSEB, 2021 (A)]

    (A) Electrons

    (B) Holes

    (C) Photons

    (D) Protons

100. The Boolean expression for OR gate is: [BSEB, 2021 (A)]

     (A) $A + B = Y$

     (B) $A \cdot B = Y$

     (C) $\bar{A} = Y$

     (D) $\overline{A \cdot B} = Y$

101. One amu is equal to: [BSEB, 2021 (A)]

     (A) $1.66 \times 10^{-27} \, kg$

     (B) $1.6 \times 10^{-19} \, kg$

     (C) $1.6 \times 10^{-31} \, kg$

     (D) $1.0 \times 10^{-27} \, kg$

102. Electron-volt ($eV$) is a unit of: [BSEB, 2020 (A)]

     (A) Charge

     (B) Potential difference

     (C) Current

     (D) Energy

103. The dimension of Planck’s constant ($h$) is: [BSEB, 2020 (A)]

     (A) $[ML^2T^{-1}]$

     (B) $[ML^2T^{-2}]$

     (C) $[MLT^{-1}]$

     (D) $[MLT^{-2}]$

104. The time in which the amount of radioactive substance becomes half is called: [BSEB, 2021 (A)]

     (A) Average life

     (B) Half-life

     (C) Decay constant

     (D) Time period

105. Light year is the unit of: [BSEB, 2024 (A)]

     (A) Distance

     (B) Time

     (C) Energy

     (D) Intensity

106. Current is produced in a closed conductor near a magnet if: [BSEB, 2024 (A)]

     (A) Only magnet is in motion

     (B) Only conductor is in motion

     (C) Both are in motion

     (D) There is relative motion between them

Revision & Mixed (107-130)

107. Device that converts mechanical energy into electrical energy: [BSEB, 2020 (A)]

     (A) Dynamo

     (B) Motor

     (C) Transformer

     (D) Induction coil

108. Ratio of peak value to $I_{rms}$ of AC is: [BSEB, 2023 (A)]

     (A) 2

     (B) $\sqrt{2}$

     (C) $1/\sqrt{2}$

     (D) 1/2

109. Velocity of light in vacuum is $c$, its value in glass ($\mu=1.5$) is: [BSEB, 2021 (A)]

     (A) $3c/2$

     (B) $2c/3$

     (C) $4c/3$

     (D) $c/2$

110. The magnifying power of a compound microscope is: [BSEB, 2020 (A)]

     (A) $m = -\frac{L}{f_o}(1+\frac{D}{f_e})$

     (B) $m = -\frac{f_o}{L}(1+\frac{D}{f_e})$

     (C) $m = -\frac{L}{f_o}(\frac{f_e}{D})$

     (D) None of these

111. Lenz’s law is related to:

     (A) Charge

     (B) Mass

     (C) Energy

     (D) Momentum

112. The working principle of a choke coil is based on:

     (A) Conservation of momentum

     (B) Self-induction

     (C) Mutual induction

     (D) Angular momentum

113. Induction coil is used to:

     (A) Measure resistance

     (B) Measure potential difference

     (C) Measure current

     (D) Operate discharge tubes

114. The power factor of a purely inductive circuit is:

     (A) 0

     (B) 1

     (C) 0.5

     (D) Infinity

115. The unit of mutual-inductance is:

     (A) Weber

     (B) Ohm

     (C) Henry

     (D) Gauss

116. Principle of operation of a dynamo is based on:

     (A) Heating effect of current

     (B) Electromagnetic induction

     (C) Induced magnetism

     (D) Induced electricity

117. Current in a coil changes from 5A to 2A in 0.1s, 50V is produced. L is:

     (A) 1.67 H

     (B) 6 H

     (C) 3 H

     (D) 0.67 H

118. The inventor of electromagnetic induction was:

     (A) Lenz

     (B) Faraday

     (C) Rumkorff

     (D) Fleming

119. Self-inductance of a circular coil (500 turns, $r=5 \, cm$) is about:

     (A) 25 mH

     (B) 50 mH

     (C) 2.5 mH

     (D) 250 mH

120. Impedance of $L-R$ circuit is:

     (A) $\sqrt{R^2 + (\omega L)^2}$

     (B) $R + \omega L$

     (C) $\sqrt{R + \omega L}$

     (D) $R^2 + \omega^2 L^2$

121. Hot wire ammeter measures:

     (A) rms value

     (B) average value

     (C) peak value

     (D) None of these

122. Why is the core of a transformer laminated?

     (A) To reduce energy loss

     (B) To increase voltage

     (C) To increase current

     (D) To increase magnetic field

123. On increasing the tube length of a microscope, its magnifying power:

     (A) Increases

     (B) Decreases

     (C) Remains constant

     (D) Becomes zero

124. Which lens is needed to correct astigmatism?

     (A) Cylindrical

     (B) Convex

     (C) Concave

     (D) Plano

125. Refractive index of glass is maximum for which color?

     (A) Violet

     (B) Red

     (C) Yellow

     (D) Green

126. What is the critical angle for diamond?

     (A) 24.41°

     (B) 48.75°

     (C) 41.14°

     (D) 37.31°

127. The limit of resolution of a healthy human eye is:

     (A) 1′ (One minute)

     (B) 1″ (One second)

     (C) 1° (One degree)

     (D) 0.5′

128. Distance between two lenses in an astronomical telescope (normal adjustment):

     (A) $f_o + f_e$

     (B) $f_o – f_e$

     (C) $f_o \times f_e$

     (D) $f_o / f_e$

129. For interference, it is necessary that both sources are:

     (A) Coherent

     (B) Of same amplitude

     (C) Of same frequency

     (D) None of these

130. The phenomenon of polarization proves that light waves are:

     (A) Transverse

     (B) Longitudinal

     (C) Progressive

     (D) Stationary